1. Field of the Invention
The present invention relates to a radiation image capturing system including a cassette having a radiation detector for detecting a radiation that has passed through a subject and converting the detected radiation into radiation image information and an external controller for receiving the radiation image information transmitted from the cassette, and a method of setting a minimum transmission radio-field intensity in such a radiation image capturing system.
2. Description of the Related Art
In the medical field, there have widely been used radiation image capturing apparatus which apply a radiation to a subject and guide the radiation that has passed through the subject to a radiation detector so as to capture a radiation image from the radiation. Known forms of the radiation detector include a conventional radiation film for recording a radiation image by way of exposure, and a stimulable phosphor panel for storing a radiation energy representing a radiation image in a phosphor and reproducing the radiation image as stimulated light by applying stimulating light to the phosphor. The radiation film with the recorded radiation image is supplied to a developing device to develop the radiation image, or the stimulable phosphor panel is supplied to a reading device to read out the radiation image as a visible image.
In the operating room or the like, it is necessary to read a recorded radiation image immediately from a radiation detector after the radiation image is captured for the purpose of quickly and appropriately treating the patient. As a radiation conversion panel which meets such a requirement, there has been developed a radiation detector having a solid-state detector for converting a radiation directly into an electric signal or converting a radiation into visible light with a scintillator and then converting the visible light into an electric signal to read a detected radiation image.
Radiation image capturing systems employing such a radiation detector are disclosed in Japanese Patent No. 3494683 and Japanese Laid-Open Patent Publication No. 2006-263339.
In the radiation image capturing system disclosed in Japanese Patent No. 3494683, radiation image information detected by a radiation detector is transmitted to a processor by way of wireless communications, and signal processing such as image processing is performed on the radiation image information by the processor.
Japanese Laid-Open Patent Publication No. 2006-263339 reveals an electronic cassette which is capable of transmitting, by way of wireless communications, a large volume of radiation image data at a high rate using a high frequency in excess of 1 [GHz].
When the cassette transmits radiation image information to an external device by way of wireless communications, the cassette consumes a large amount of electric power. Accordingly, a battery incorporated in the cassette for energizing the cassette is relatively large in size, making the cassette large in volume and weight.